The present invention deals with a probe for use in apparatus that analyzes timing and engine speed of a diesel engine.
In analyzing the timing events in an internal combustion engine, determination is made of the number of degrees of crank shaft rotation between the time the piston in a selected cylinder reaches its so-called "top dead center" position and the time that combustion takes place in that cylinder. Automobile manufacturers commonly specify the number of degrees at a specific engine speed. Thus, the events of top dead center and combustion must be determined. One type of probe has been developed that enables sensing both events. In a diesel engine, the glow plug for a selected cylinder is replaced with such probe. The probe includes means for conducting light produced during the combustion event. It also includes means for conducting microwave energy into the cylinder and conducting from the cylinder microwave energy modulated therein during engine operation. Such a probe is described in U.S. Pat. No. 4,337,648, issued Jul. 6, 1982 and assigned to Jodon Engineering Associates, Inc. Jodon has made and sold a probe like that shown in the patent but somewhat different.